How does rising atmospheric CO2 affect marine organisms?

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Are Greenhouse Gas Emissions Enhancing Ocean Productivity?
Dupouy, C., Neveux, J., Subramaniam, A., Mulholland, M.R., Montoya, J.P., Campbell, L., Carpenter, E.J. and Capone, D.G.  2000.  Satellite captures Trichodesmium blooms in the southwestern tropical Pacific.  EOS, Transactions, American Geophysical Union 81: 13, 15-16.

What was done
The authors note that marine biology may play a major role in regulating atmospheric CO2 over geologic time.  They state, for example, that during interglacial periods, N2 fixation in the world's oceans is generally low, due to a low supply of iron compared to that of glacial periods.  This state of affairs thus leads to low surface productivity and little CO2 removal from the atmosphere.  Hence, in an attempt to better understand where the world's oceans stand today in this regard, they describe some of their ongoing research projects geared to investigate this question.

What was learned
The evidence the authors have acquired to date suggests that marine N2 fixation may be much greater than what has generally been thought to be the case.  In particular, they say that several Trichodesmium species of N2-fixing cyanobacteria have "a nearly ubiquitous distribution in the euphotic zone of tropical and subtropical seas and could play a major role in bringing new N to these oligotrophic systems."  And this feat, in turn, "could play a significant role in enhancing new production."

What it means
The significance of these findings - which are still undergoing critical evaluation - are perhaps best appreciated in light of the recent report of Pahlow and Riebesell (2000), who detected changes in deep-ocean Redfield ratios indicative of increasing nitrogen availability to the oceans over the last fifty years, along with an increasing export production that is resulting in ever-increasing oceanic carbon sequestration.  The latter investigators suggest that the growing supply of nitrogen has its origin in anthropogenic activities that release nitrous oxides to the air; but we here speculate that it may also be partially a consequence of the rising CO2 concentration of the atmosphere, by way of its potential to enhance aquatic productivity, including N2 fixation, as it does on land.  Clearly, this area of research is pregnant with possibilities that cry out to be studied in more detail.

Pahlow, M. and Riebesell, U.  2000.  Temporal trends in deep ocean Redfield ratios.  Science 287: 831-833.

Reviewed 1 March 2000